According to Ablogtowatch their measurements of the 42:
It is interesting to see how the proportions of the 42mm variant has remained exactly the same as that of the larger model. It is extremely difficult to tell the two apart, when judging from the images. That said, the Hublot Big Bang Unico Titanium Ceramic 42mm is a lot larger than the 42mm figure in its name would lead you to believe. The only way this watch measures 42mm is from the 10 o’clock position of the case profile to the edge of the bezel (!) at 4 o’clock.
At 4 o’clock, the pusher enters the case at a point where the polished titanium case profile just stops. Sure, there is a ring around the pusher, but that, in Hublot’s mind, doesn’t count. So yeah, this watch does measure 42mm from 10 o’clock to the edge of the bezel at 4 (and obviously from 8 to 2 o’clock all the same). But that’s it.
Lug-to-lug, the case measures 52mm, which is at the very top end of lug-to-lug measurements among 42mm watches — they normally rank between 48mm and 50mm, at most. Then, there is the issue of the integration of the strap and their shape. They extend far and away from the case and never exactly downward, adding very substantially to the lug-to-lug visual heft of the watch. It creates the impression of a tall and narrow watch that doesn’t yet look disproportionate, but it’s damn close to being just that.
>Size: 42mm-wide on paper — wears more like 44mm-45mm watches.
Thickness of the case should be: 14.5mm